On a pipeline of a blood cell analyzer, a test tube rack carrying test tubes (with blood samples) is transported from a loading platform to a detecting area of the blood cell analyzer by a transporting belt along a track. The test tube rack is shifted one step each time so that each test tube carried on the test tube rack is passed through a test tube detector and a sample needle one by one to let the analyzer detect the reference code of the test tube and conduct sample collections. The distance of one shift step is defined as the width of one test tube unit. For certain reasons, such as lost steps of a stepper motor, the test tube rack may shift to a wrong position (the test tube fails to move to a predetermined position), which would cause wrong reference codes to be detected by the test tube detector and wrong samples to be sampled by the sample needle, so as to make test results fail to match the right sample provider (patient). Obviously, such mis-operations would cause many risks in clinical settings.
To avoid the mentioned clinical risks, an operation for testing whether the test tube rack is shifted to the right position in the pipeline should be conducted. A warning is raised when the test tube rack is shifted to the wrong position. In the conventional method, by distinguishing the differences of reflected signals from different areas, an optical detector is used to detect a feature area on the back side of the test tube rack to implement the above position detection.
Referring to FIG. 1, a middle portion between two test tube holders of the back side of test tube rack 101 is processed to form a groove with a 6 mm depth. The test tube rack 101 is formed as a through hole with a rectangular shape front to back at the location of the test tube holder of the test tube rack 101. A narrower edge 103 is defined between a groove 104 and a rectangular hole 105. The optical detector aims the center of the groove 104 by adjusting positions. The test tube rack 101 is shifted a width of the test tube holder one time then the optical detector is directed to aim at the next groove from the currently aimed groove. In this process, the optical detector detects five feature areas; they are a first groove, a first edge, a test tube, a second edge and a second groove respectively (the test tube is detected since it is located at the rectangular hole of the rack). Because the distance between the groove or the test tube and the optical detector is far, the reflected light from the groove or the test tube to the optical coupler is weak. The reflected light from the edge to the sensor is strong since the distance between the edge and the optical coupler is close. Therefore, the feature of the reflected signal shown in the shifting process would be presented as low—high—low—high—low.
In general, an absolute value determination method is applied in the above signal detection. In the absolute value determination method, a threshold voltage is marked between a groove signal and an edge signal at first, and each voltage signal generated in the sifting process of the test tube rack is used to compare with the threshold voltage. If two voltage signals with an impulse higher than the threshold voltage are detected, it means two edges of the rack have passed through. In other words, the above result proves the rack has shifted to the right position. However, since the detection areas of the sensor include the test tube, the reflected signals reflected in certain angles from a glass test tube with a sample inside could be over the threshold value to generate a false impulse if a tag is not pasted on the test tube. Even when a tag is pasted on the test tube, the surface of some specific tag types may be too bright and cause the reflected signals from the tag that are still too strong to generate a false impulse. Therefore, multiple impulses higher than the threshold voltage may be detected between two grooves so as to cause a false negative determination even when the test tube rack is shifted to the wrong position. Under the above, conventional skills for detecting the shift state of the test tube rack are not reliable; it still contains chances for wrong or missing detections, so the clinical risk still exists.
In addition, for figuring out clinical issues, such as temperature variances, sensor aging, and errors of the track (the track has a certain width; a 1 mm tolerance should be defined under the above width) causing the value of reflected signals floating over the threshold voltage to affect the viability of the detecting result, a high-performance sensor/optical detector is the only choice to implement the above conventional solution since only the optical detector has enough sensitivity to satisfy the high demand of the above solution. The purpose for applying the optical detector is to enlarge the differences between the groove signal and the edge signal as much as possible. However, the optical detector is so expensive that it causes the cost of the blood cell analyzer to be significantly high, which restricts the implementation of the detection technology for detecting displacement issues of the test tube rack.